AN AUTOMATED RAPID TEST FOR Escherichia coli IN MILK

Abstract

ABSTRACTA method was developed to rapidly enumerate Escherichia coli in milk, using a Technicon Auto Analyzer II system. The automated system was used to assay for the presence of glutamate decarboxylase (E.C. 4.1.1.15), which is found only in E. coli and a few other bacterial species that are highly unlikely to be found in milk Coliiorms other than E. coli were shown not to have this enzyme. This system was capable of detecting as few as 50,000 E. coli organisms/ml. The most probable number (MPN) technique was combined with the automated system to quantitate E. coli in milk With pure cultures it was possible to determine the positive and negative MPN tubes in 8 hr, but a 10‐hr incubation was required for the analysis of milk samples. Since the enzyme is specific for E. coli, the nonselective medium trypticase soy broth and the mildly selective medium lauryl tryptose broth were used in the MPN tubes. It was shown that these media allowed the growth of heat‐injured organisms and the detection of organisms that could not be detected using violet red bide agar. The three advantages of this test over the current violet red bile plating procedure are (1) it is more rapid, (2) it is specific for E. coli and (3) it enumerates process‐injured organisms.